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<html lang="en">
  <head>
    <meta charset="UTF-8" />
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    <meta name="viewport" content="width=device-width, initial-scale=1.0" />
    <title>Document</title>
  </head>
  <body>
    <script>
      // 外部作用域没办法直接访问内层的变量
      //   function out() {
      //     let a = 10
      //   }
      //   out()
      //   console.log(a)

      // 作用1：可以让外部作用域访问到函数内部的变量
      function out() {
        let a = 10
        function inner() {
          console.log(a)
        }
        return inner
      }
      //   fn===>out()===>inner() {
      //       console.log(a)
      //     }
      let fn = out()
      fn()

      //   简写
      function out1() {
        let a = 10
        return function inner1() {
          console.log(a)
        }
      }
      let fn1 = out1()
      fn1()
    </script>
  </body>
</html>
